I think 12mm and 15mm would put you in a situation where you'd have to do some fender modification.
Front ET35 - 15mm spacers = 20mm new offset
Rear ET33 - 12mm spacers = 21mm new offset
That would look gorgeous IMO but like the previous have said, 10mm would probably be on the safe side.
Judging by the pictures it looks like you can do lower though.